Automatic fire control for coal fired furnace



J. A. SCHUSS 5 Sheets-Sheet l [NVE/V702 JAC/(A. SCI-[USS ATTORNEYAUTOMATIC FIRE CONTROL FOR COAL FIRED FURNACE Aug. 6, 1968 Filed Aug.

Aug. 6, 196s 1A. SCHUSS 3,395,657

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AUTOMATIC FIRE CONTROL FOR COAL FIRED FURNACE P E Q Y N lL u o N N N NCp P fp A /J n a (e a N v N a N r y s Q N N '3 n d T T N 2 3 INVENTOR. 3o n S n w JAcKAcHuss N N N N ATTOEN E Y United States Patent O "ice3,395,657 AUTOMATIC FIRE CONTROL FOR COAL FIRED FURNACE Jack A. Schuss,Hartford, Conn., assignor to Combustion Engineering, Inc., Windsor,Conn., a corporation of Delaware Filed Aug. 1, 1966, Ser. No. 574,511 16Claims. (Cl. 110-22) ABSTRACT OF THE DISCLOSURE A control system foroperating the burners of a multiburner, coal-fired system toautomatically place groups of burners in service in response to changingload requirements on the power plant. This system comprises a digitalcontrol effective to selectively place individual coal pulverizing millstogether with their associated groups of burners in service when loaddemand on the power plant so requires. The system further includes meansto monitor the operation availability of each mill and its associatedburner group and to place in service only that mill and group of burnerscapable of increasing the total heat output of the burner system.

The present invention relates to automated fuel ring systems for vaporgenerators. More particularly, the invention concerns anelectro-mechanical control system effective to automatically place theburners of a multiburner, coal-fired vapor generator burner system inservice in response to increase in load demand requirements.

In recent years it has become accepted practice to operate the fuel ringequipment of thermal power stations from a centralized control wherevarious instruments capable of indicating the state of unit operation,such as gauges, indicating lights and recorders, are assembled togetherwith switches that are effective to control the operation of the fuelfiring equipment. In such installations the boiler operator visuallysenses the condition or state of system operation and, when digressionsfrom the desired state of operation occur, manually actuates theappropriate control switches for the purpose of controlling the firingsystem to offset these changes. The decision making in theseinstallations remains with the operator and therefore is subject tohuman error. As the size and capacity of vapor generating stationsincrease, the number of sensing apparatus and the number of componentsthat must be controlled are greatly multiplied thereby rendering it morediflicult for the operator to safely and efficiently control theoperation of the power plant system. There is a growing demand,therefore, for unit automation to relieve the operators burden and toensure plant safety and efficiency of operation. It is to this end thatthe present invention is directed.

The present invention is contemplated for use in power plants comprisingvapor generators employing coal as the principal fuel. The fuel firingsystem of such units consists of a coal burner system that is operableover the normal load range of the vapor generators and an ancillary oilburner system that provides heat for warming up the unit prior to itsbeing put on the line. The oil burner system is also operative toprovide ignition energy for igniting each of the coal burners as theyare placed in service. The coal pulverizing mills that supply coal tothe burners are considered as being part of the fuel firing systeminasmuch as burner operation is dependent upon and controlled by theoperation of the pulverizing mills.

The control system of the present invention, together with conventionalcombustion controls, operates to provide the control and regulation ofthe fuel tiring system of large capacity vapor generators with a minimumof 3,395,657 Patented Aug'. 6, 1968 manual supervision. While thecombustion controls are of an analog type and operative to regulate theoperation of the fuel burners in service in response to varying loaddemand, the instant control system is an improved form of digitalcontrol that is effective to safely and effectively place burners inservice when the load demand requirements of the unit so require.

According to the invention the coal burners and the oil burners thatcomprise the firing system are each arranged in groups with the groupingbeing such that each group of coal burners is capable of being ignitedby an adjacent group of oil burners. The control system of the inventionprovides means responsive to the need for placing groups of coal burnersinto operation for placing an appropriate group of oil burners inservice and thereafter, initiating the startup of the coal pulverizingmill which supplies coal to a group of burners that are ignited by theoperating group of oil burners. Means are also provided to oversee theoperational capability of the oil burners and mills and to initiateoperation of a group of oil burners only when it is itself operationaland the mill associated with the coal burners ignited by it isoperational. Additional means are provided to automatically place analternative group of oil and coal burners in service in the event thedesired groups are incapable of being placed in service.

The various objects and advantages of the invention will be evident fromthe following description when read in light of the accompanyingdrawings in which:

FIGURE 1 is a schematic representation of a power plant employing thepresent invention;

FIGURE 2 is a schematic representation of a typical firing corner in thevapor generator of FIGURE 1;

FIGURE 3 is a schematic representation of a typical coal pulverizingmill contemplated for use in the present invention;

FIGURE 4 is a schematic representation of the fuel oil system utilizedin carrying out the present invention;

FIGURE 5 is a circuit diagram, shown somewhat schematically, of thePulse Initiation Circuit of the present -control system;

FIGURE 6 is a circuit diagram of the Oil Elevation Selection Circuit;

FIGURE 7 is a circuit diagram of the Mill Selector Circuit;

FIGURE 8 is a typical Mill Start Control Circuit;

FIGURE 9 is a typical Burner Counting Circuit contemplated for use inthe present invention;

FIGURE 10 is a schematic representation of a Mill-in- Service FeedbackRelay employed in the instant invention.

General arrangement Referring now to the drawings, FIGURE 1 illustratesa thermal power plant 10 that is operated in accordance with the presentinvention. It comprises a vapor generator 12 that is operativelyconnected to a steam turbine 14 which, in turn, drives an electricgenerator 16. Analog controls in the form of a Steam Output Control 18and a Combustion Control 20 are employed to control plant output inresponse to changing load demand. These controls are of knownconstruction and do not form part of the present invention.

As shown, the vapor generator 12 includes a furnace 22 lined with fluidconducting tubes 24 within which high temperature vapor is created andpassed through line 26 to lthe turbine 14. In line 26 is located a vaporregulating valve 28 operated in response to the Steam Output Control .18to regulate the supply of vapor to the turbine. Steam line 26 alsocontains a pressure sensing element 30 adapted to transmit a signal tothe Combustion Control 20 which is effective to adjust liquid and fuelinput to the vapor generator 12 in order to satisfy the demandrequirements of the turbine.

The tiring system of the vapor generator includes burner assemblies 32arranged to operate within the furnace 22. In the disclosed embodimentof the invention the burner assemblies 32 are disposed in each of thefour corners of the furnace with the burners being adapted fortangential firing. Each assembly 32 consists of alternately verticallyspaced pulverized coal burners 34, oil burners 36 and auxiliary airnozzles 38. The structural details of these burner assemblies aresimilar to those disclosed and described in U.S. Patent No. 2,697,422issued Dec. 21, 1954, to Armacost and a description thereof is notdeemed necessary herein for an understanding of the present invention.The burners are deployed in eleven elevations, indicated in FIGURES 1and 2 as Elevations A through L. Each elevation comprises four burnernozzles, each disposed at one of the corners of the furnace 22.Elevations A, G and L comprise those nozzles 3S adapted to supplyauxiliary combustion air to the furnace; Elevations B, D, F, H and Kconsist of coal burners 34 and Elevations C, E and I consist of oilburners 36 together with their associated pilot torches 40. As shown,each elevation of coal burners 34 is supplied with pulverized coal bymills 42 and their associated equipment through coal supply lines 44having burner inlet vales 46 disposed therein for controlling the flowof coal to each of the burners. Each elevation of oil burners 36, on theother hand, is supplied with fuel oil through an oil supply line 48 thatis connected to a main oil line 50.

Coal Supply System In FIGURE 3 is illustrated a schematic representationof a typical coal supply system contemplated for use in the inventionfor supplying pulverized coal` to the burners 34 of each of the coalburner elevations B, D, F, H and K. It comprises a coal pulverizing mill42 which receives raw coal from a collection hopper (not shown) by meansof a feeder 52 driven by a variable-speed motor S4. Lines 56 and 58,containing power-operated feeder inlet and outlet gate valves, `60 and62 respectively, connect the feeder 52 between the hopper and the -mill42. The rate at which coal is supplied to the burners 34 is controlledby the Combustion Control which operates to vary the speed of motor 54and thereby regulate the amount of raw coal passed to the mill 42 andthence to the burners. As shown, a tachometer 64, or the like, may beemployed for transmitting a coal flow measurement feedback signal to theCombustion Control 20. Hot air is supplied to the mill 42 through duct66 having a power operated gate valve 68. This air serves both to drythe coal within the mill and to convey the pulverized coal fines to theburners 34. The latter function is effected by means of an exhaust fan70 connected between the mill 42 and the line 44. A power-operated milldischarge valve 72 is connected in line 44 downstream of the exhaust fan70 for initiating or terminating the admission of pulverized coal to theline. Mill air temperature is controlled by the admission of cold airthrough duct 74 with its power-operated gate valve 76 to the hot airduct 66 upstream of the mill. The total air flow to the mill iscontrolled by the Combustion Control 20 through damper 78 while the millair temperature is controlled by the regulation of hot and cold airdampers 80 and 82 through a Mill Air Temperature Controller 84 whichreceives a feedback signal from an appropriately positioned mill airtemperature measurement device 86.

Oil Supply System In FIGURE 4 there is shown a schematic representationof the fuel oil system employed in the preferred embodiment of theinvention. It comprises a main oil 50 that is connected in common withall of the oil burners 36 in each oil burner elevation C, E and I.Positioned in the line 50 is a power-operated oil regulating valve 90that is adapted to regulate the amount of fuel supplied to the burners36 under the control of the Combustion Control 20. Actual oil ow throughthe line 50 is determined by a flow sensor 92 whose signal operates as afeedback to the Combustion Control. A bypass flow regulator 94 operatesin parallel with the valve 90, lits purpose being to ensure the presenceof a minimum amount of oil line pressure to the burners 36 regardless ofthe position of the valve when the oil system is in operation. Thisminimum oil pressure is determined to be that which is required toeffect automation of the oil supplied to the burners in order that itcan be readily ignited. In the instant example an oil pressure ofapproximately p.s.i. is considered to be adequate for this purpose.

The line 50 supplies oil to each elevation of oil burners, C, E and J,through take-off lines 48 which each have an associated power-operatedadmission valve 98. Likewise, each oil burner 36 is equipped with anassociated admission valve 100 that is operative to terminate operationof each burner upon the occurrence of an unsafe condition as determinedby an associated control device (not shown). Ignition of the burners 36is effected by means of a pilot torch 40 associated with each burner.For the sake of brevity, only one such torch 40 is shown in FIG- URE 4.Each pilot torch 40, which is commonly gas-operated, has an associatedfuel valve 102 and spark ignitor 104 that are actuated when it isdesired to provide ignition energy for the oil burners 36.

In the herein disclosed arrangement the oil burner system of FIGURE 4 isoperative to provide combustion energy to the furnace 22 during warm-upand also to provide ignition energy for the coal burners 34 duringnormal vapor generator operation. During the warm-up phase of unitoperation the oil burner system is automatically controlled by anindependent control sub-loop that is effective to place each oil burnerelevation in service in a prescribed sequence such that vapor generatortemperature is gradually increased up to its minimum operatingtemperature. The control sub-loop employed in a preferred embodiment ofthe invention is substantially the same as that embodied -in co-pendingU.S. patent application Ser. No. 484,061 to the same inventor filed Aug.31, 1965, now Patent No. 3,341,118, and a complete description thereofis therefore not required in this application. For the sake ofdescribing the instant invention, it is only necessary to understandthat when the vapor generator goes into operation upon completion of thewarm-up procedure that terminates with the phase synchronization of theelectric generator 16, all the oil burner elevations are considered tobe in operation under thecontrol of the Combustion Control 20 and theyremam in operation until such time as the generation of combustionenergy generated in the furnace 22 is taken over by the coal burnersystem, the control of which is the subject of the present invention.

Control System Therefore, according to the present invention means areprovided to safely and effectively place each elevation of coal 'burnersB, D, Fl H and K in service automatically Without the need of manualsupervision. This means comprises a fixed program digital control thatis effective to place the coal pulverizing mills 42 associated with eachcoal lburner elevation in service in 4response to an increase in vaporgenerator load demand. The mills 42 are placed 1 n servlce according toa predetermined sequence, which, m the preferred embodiment, isaccording to the sequence D-B-F-H-K. The control means of the presentinvention is operative to scan the operational availability of each mill42 and to place it in operation only when conditions permit its beingplaced in operation. In the event one or more of the mills in thesequence are incapable of safe operation or whose availability forservice has been disrupted, as for example, for maintenance purposes,the control system is operative to seek out another -mill in thesequence that can be operated and place it in service in order tosatisfy the indicated increase in load demand.

While in the herein described embodiment of the invention the fuel ringsystem is shown as containing five elevations of coal burners 34, threeelevations of oil burners 36 and three elevations of air nozzles 38 witheach elevation comprising elements disposed at each of the four cornersof the furnace 22, it is to be understood that such arrangement has beenemployed for the purpose of illustration only and that a greater or lessnumber of elevations can be employed according to the present teaching.

Fire Control Going now to the power plant control system, in FIG- URE 1there is shown a Fire Control 106 which is adapted to control theoperation of the mill 42 which in turn governs the operation of the coalburners 34. The Fire Control 106 yfunctions independently of theCombustion Control 20, the latter being an analog type of control andresponsible for the regulation of operation of the mills and burners inresponse to condition changes in the system while the former is a fixedprogram digital controller whose control functions are superimposed uponthose of the Combustion Control` More particularly, while the CombustionControl is effective to regulate the supply of working medium, namelyfuel and water, to the vapor gener-ator in response to load changes, theFire Control 106 is independently effective to alter the number of coalpulverizing mills 42 and thus the number of coal burners 34 that areplaced in operation. It is the objective of the Fire Control 106 toplace mills 42 and burners 44 in service and of the Combustion Control20 to regulate the operation of those mills and burners once they are inservice. In achieving this objective, the Fire Control 106 functionsfirst to determine when the need for placing additional burners inservice arises. After having determined that additional burners must beinstalled in service, the Fire Control 106 is operative to determine`which of the mills 42 are capable of being placed in service takinginto account the availability of sufficient ignition energy from theassociated oil elevations with which to ignite the coal supplied to thecoal burners and the operability of the respective mills. Thereafter thecontrol is operative to take appropriate steps to place the selectedmill and coal burner elevation in service. This is accomplishedaccording to a predetermined sequence of mill actuation. If, however,the selected mill and burner elevation cannot be safely operated, theFire Cont-rol is effective to select the neXt mill in the sequence andto initiate its start-up, and so on, until the load demand has beensatisfied.

Pulse Initiation Circuit The Fire Control 106 `comprises three principalcontrol sub-loops, namely, the Pulse Initiation Circuit (FIG- URE 5),lche Oil Elevation Start Circuit (FIGURE 6) and the Mill Start Circuit(FIGURE 7). The Pulse Initiation Circuit as shown in FIGURE 5 consistsof a seriesparallel circuit connected across the hot and ground lines ofan electric source and is effective, upon completion of the circuit, toenergize a pulse timer 108. As shown, the circuit comprises a startswitch 110 that is manually operated to place the firing control inoperation. The circuit also comprises parallelly connected lines 112 and114, the line 112 being operative to govern unit operation prior to anymill being placed in service when one set of conditions is required toplace a mill in operation and the line 114 being operative when one ormore of the mills is operating and another set of conditions isapplicable. Line 112 contains a series connection of switches 116, 118and 120. Switch 116 is a normally open, manual or relay operated, switchassociated with the turbo-generator installation and actuated to theclosed position when the generator is synchronized and the unittherefore ready to be placed on the line. Switches 118 are normallyclosed, relay actuated switches associated with each of the mills 42 andtherefore sufiixed in the drawing with letters B,

D, F, H and K indicating the mill with -which each is associated. Inoperation each of the switches 118` will remain closed until such timeas its lassociated mill is placed in operation whereupon the appropriateswitch is actuated to its open position by means of a feedback relay 272(FIGURES 8 and 10) to thereafter render line 112 ineffective to pass anelectric current to the pulse timer. Switch 120 is a normally open,relay operated switch associated with the oil flow sensor 92 in the mainoil supply line 50. The arrangement is such that an operating relay (notshown) 'will be actuated to close the switch 120 at a predetermined oilflow setting, that setting corresponding to an oil flow to the burners36 having a heating potential that corresponds to the heat potential ofthe coal supplied by one mill operating at its minimum output plus theheat potential of an associated oil tburner elevation that will beutilized to ignite the coal supplied by the mill. The purpose of thiscontrol element is to ensure the maintenance of a balance of heat withinthe furnace 22 when the source of combustion energy changes from oil tocoal.

Line 114 contains a series connection of switch 122 and parallellyconnected switches 124. Switch 122 is a normally open, relay actuatedswitch that is closed when the average loading of all the operatingmills 42 is at least as great as of the total operating capacity of themills. This switch is actuated by a relay (not shown) controlled by theCombustion Control 20 to operate when the average output of the numberof mills in 0peration equals 80% of their combined capacity asdetermined by feedback signals obtained from the tachometer '70associated with each mill feeder 58. Switches 124, appropriatelysufiixed with an indication of the respective mill with which each isassociated, are normally open, relay operated switches that are closedwhen their associated mill is placed in operation. Thus line 114 willgovern the operation of the Fire `Control 106 after at least one coalmill 42 has been placed in operation.

The Pulse Initiation `Circuit also contains parallelly connectedswitches 126B, 126D, 126F, 126H and 126K connected in series with lines112 and 114. The switches 126 are normally open switches operated byrelays 218 (FIGURE 9) and associated with each of the respective mills42 to be closed when the associated mill is available for service. Byavailable for service is meant that all of the requirements for safemill operation have been satisfied as indicated by the actuation ofappropriate feedback relays to be discussed hereinafter. An additionalrequirement that must be met before a mill is considered to be availablefor service is that the mill is not already in service. This conditionis also determined through the actuation of an appropriate feedbackrelay that will be hereinafter discussed.

The Pulse Initiation `Circuit further contains a series connection ofparallelly connected switches 128C, 128B and 128] which are normallyclosed switches associated with each of the respective oil burnerelevations and adapted to be actuated to an open position when the aS-sociated burner elevation is incapable of being placed in service. Theswitches 128 can be actuated to an open position manually, as when it isdesired to perform maintenance on one of the respective burnerelevations or automatically by means of a control relay. The system isarranged such that automatic actuation of the switches 128 will occurwhen the number of operable oil burners 36 in each of the elevations C,E and J is insufficient to ignite the coal burners 34 of an associatedcoal burner elevation.

For this purpose, burner counting circuits, such as that shown in FIGURE9, are employed to prevent actuation of an entire oil burner elevationwhenever more than one of the elevations four burners 36 areinoperative, it having been determined that if three of the four oilburners in each elevation are operable the elevation can provide asufficient amount of ignition energy to ignite all of the coal burners34 of an associated coal burner elevation. As shown, the countingcircuit comprises a series-parallel connection of normally open switches130 that are each associated with one of the four burners that comprisea given elevation. For the purpose of description, the numerals 130 aresutlixed with appropriate letters, a, b, c and d, to indicate the burnerwith which each is associated. The switches 130 in the preferredembodiment are in the form of limit switches actuated in response tomovement of each burner valve 100 to be opened when the valve is openthereby indicating that the associated burner is operating. Thus whenmore than one valve G fails to open, an electric circuit will becompleted through the appropriate switches 130 to actuate the relay 132,thereby opening its associated switch 128 in the Pulse InitiationCircuit of FIGURE 5. As shown, the relay 132 is also the operator ofswitches 156, 158, 182 and 184. The function of these switches is toprovide feedback signals indicating the operability of the associatedoil burner elevation to the Oil Elevation Selection Circuit (FIGURE 6)and the Mill Selection yCircuit (FIGURE 7) respectively. A more detailedexplanation of the operation of these switches is contained hereinafter.

The pulse timer 108 which is operated by the Pulse Initiation Circuitmay be in the form of a constant speed, synchronous motor that drives acam element 134 adapted to intermittently actuate switch 136, which inturn intermittently energizes relay 138. The motor operates at the rateof one revolution per minute and the switch 136 is closed for a durationof two seconds in each revolution. Thus the relay 138 is pulsed at therate of once every minute for two seconds duration when the pulse timer108 is energized. Pulsation of the relay 138 operates to simultaneouslyclose switches 140 and 142 which are the actuating elements of the OilElevation Selection Circuit (FIGURE 6) and Mill Selection `Circuit(FIGURE 7) respectively.

Oil Elevation Selection Circuit The `Oil Elevation Selection Circuitshown in FIG- URE 6 is operative to transfer the pulse generated by thepulse timer 10S to the operating members of one of the oil burnerelevations to initiate operation of that elevation. The circuit containsthe pulsing switch 140 operated by relay 138 connected to threeparallelly con nected oil elevation operator relays 154C, 154B and 154].The circuit arrangement is such that the pulsed closure of switch 140will pulse only one of the relays 154 to place its associated oilelevation in service. In the disclosed embodiment of the invention it isdesirable to have oil elevay tion C, which provides ignition energy toadjacent coal elevations B and D, placed in service lirst, followed byoil elevation E, serving coal elevations D and F, and then oil elevationJ serving coal elevations H and K. By means of the circuit arrangement,closure of pulsing switch 140 will actuate relay 154C unless oilelevation C is incapable of being placed in service either because ithas been locked out of service or the mills associated with coalelevations B and D are both not available for service. If relay 154Ccannot receive the pulse then relay 154B stands next in the sequence toreceive it to actuate the burners 36 of oil elevation E. Similarly,relay 154E will receive the energizing pulse as long as it is not itselflocked out of service or its associated mills 42D and 42F are notavailable for service. If neither relay 154C nor 154E is actuated by thepulse then relay 154] will receive it to place one of its associatedmills 42H or 42K in service. The circuit arrangement to perform thisfunction, as shown in the ligure, is a relatively simple series-parallelarrangement of switches 156, 158, 160 and 162. For the sake of claritylike switches are assigned similar numerals but are sutxed withappropriate letters to indicate the elevation with which each isassociated. Switches 156 are operated by the same burner countingcircuit relay 132 and have the same sense as switches 128 in the PulseInitiation Circuit of FIGURE 5 and are therefore closed when theassociated oil elevation is not locked out of service. Switches 158,also operated by relays 132, have the opposite sense from switches 156and are therefore closed when switches 156 are open and vice versa.Closure of switches 158 indicates that the associated oil elevation islocked out of service and therefore not capable of being placed inoperation. Switches are normally open switches that are operated by MillAvailable Relay 216 (FIGURES 8 and l0) and have the same sense asswitches 118 in the Pulse Initiation Circuit of FIGURE 5. These switchesare thus closed when the associated mill 42 is available for service andrelay 216 energized. Switches 162, also operated by relay 216, have asense opposite from that of switches 160 and are therefore closed whenswitches 160 are open and vice versa. Closure of switches 162 indicatesthat the associated mill is not available for service.

As shown, the Oil Elevation Selection Circuit comprises three parallellyconnected sub-circuits 164, 166 and 168 each being effective to transmitthe pulse generated by the momentary closure of switch 140 to one of therespective Oil lElevation Operator Relays 154C, 154B and 154].Sub-circuit 164 contains a series connection of switch 156C withparallelly connected switches 160B and 160D. Therefore electric currentwill pass to relay 154C upon the pulsed closure of switch 140 if oilelevation C is not locked out of service and either mill 42B or 42D isavailable for service. Sub-circuit 168 contains a similar connection ofswitches 156B, 160D and 160F which permits relay 154B to accept thepulse as long as oil elevation E is not locked out of service and eitherof those mills, 42D or 42E, supplying the coal burner 34 ignited by theburners 36 of oil elevation E is `available for service. It alsocontains, however, a series-parallel arrangement of switches 158C, 162Band 162D that must deline a current path through the sub-circuit beforerelay 154B will be pulsed. Thus, relay 154E will accept the pulsegenerated by the closure of switch 140 only if oil elevation E is notlocked out of service and either of the mills, 42E or 42F, are availablefor service but also contingent upon the fact that oil elevation C isnot locked out of service as evidenced by closure of switch 158C or bothmills 42B and 42D are not available for operation as evidenced byclosure of switches 162B and 162D.

Sub-circuit 168 contains a similar connection of switches 156], 160H and160K, the closure of the former plus one of the latter two therebypermitting relay 154] to be pulsed. This sub-circuit, however, alsocontains a seriesparallel arrangement of switches 158 associated withthe other oil elevations C and E, together with switches 162 associatedwith mills 42B, 42D and 42E, which, as shown, will permit passage of thepulse to the relay 154] only if conditions exist that prevent both ofthe other relays 154C and 154B from being pulsed.

Mill Selection Circuit The Mill Selection Circuit illustrated in FIGURE7 functions to select one of the mills 42 to be placed in operation whenconditions require the addition of another coal burner elevation inservice. The circuit comprises four parallelly connected sub-circuits170, 172, 174 and 176 which are each effective to transmit the pulsegenerated by the momentary closure of switch 142 to one of therespective mill operator relays B, 180D, 180F, 18m-I and 180K. Thearrangement is such that the pulsed closure of switch 142 by the pulsetimer relay 138 will be transmitted to only one of the relays 180 toplace its associated mill 42 and coal burner elevation in service. Inthe disclosed embodiment of the invention the desired sequence of coalburner elevation start-up is in the following order: D-B- F-H-K. Thusthe circuit arrangement shown in FIGURE 7 is such that relay 180D isadapted to be pulsed first, and, if the associated coal burner elevationD is incapable of being safely placed in service, either because thereis insuiiicient ignition energy available from the adjacent oil burners36 or the mill 42D is not available lfor service, the pulse will be nextadapted for reception by relay 180B, and so on through the sequence. TheMill Selection Circuit is a series-parallel arrangement of switches 182,184, 186 and 188. Again for the sake of description, like switches areassigned similar numerals suxed with appropriate letters to indicate theelevation with which each is associated. Switches 182 are normally openswitches operated by burner counting circuit relays 132 (FIGURE 9) andare closed when the relay 132 is de-energized thereby indicating atleast three of the four burners in the associated oil burner elevationare in service and that sufficient ignition energy will be available toignite the coal issuing from the burners 34 when the respective millsare placed in service. Switches 184 also are operated by relays 132, buthave a sense opposite from that of switches 182, thus the former will beclosed when the latter is open and vice versa. Therefore closure ofswitch 184 indicates that the associated oil elevation cannot providesuicient ignition energy to ignite the adjacent coal burners. Switches186 are normally open switches operated by relays 216 (FIGURES 8 and 10)and have the same sense as switches 118 and 160 referred to above.Closure of switches 186 therefore indicates that the associated mill 42is available for service. Switches 188, also operated by relays 216, buthaving a sense opposite from that of switches 186, are therefore closedwhen the associated mill 42 is not available for service.

As shown in FIGURE 7, each of the sub-circuits, 170 through 176, areeffective to transmit the pulse generated by closure of switch 142 toone of the mill operator relays 180. Sub-circuit 170, associated withrelay 180D, contains a series connection of switch 186D with parallellyconnected switches 182C and 182E. Thus current will pass through thecircuit to relay 180D upon the pulsed closure of switch 142 if at leastone of the two oil burner elevations, C or E, adjacent coal burnerelevation D is in service and mill 42D is available for service.Subcircuit 172, associated with relay 180B, contains a series connectionof switches 182C, 186B and 188D. Thus, the associated relay, 180B, willbe energized when oil elevation C is proven to be in service by closureof switch 182C and mill 42D is not available for service but mill 42B isso available as indicated by closure of switches 188D and 186B,respectively. Sub-circuit 174 contains switches 182L, 186F and 188Dwhich are connected in series with parallelly connected switches 184Cand 188B. Relay 180F will therefore be energized upon closure of switch142 if oil elevation C is not in service or, if in service, neithermills 42B or 42D are available for service, provided oil elevation E isproven to be able to supply suicient ignition energy to ignite the coalsupplied to the burners 34 of one of the associated coal elevations andprovided also that mill 42F is available for service. Subcircuit 176 isarranged to operate both mill operator relays 180H and 180K. Theseries-parallel arrangement of the various switches 182, 184, 186 and188 is such that relay 180H will be energized if its associated mill 42His -available for service and associated oil elevation J is deliveringsuicient ignition energy by any one of the four routes defined by thearrangement. First, current will pass to the relay through the linedened by switches 184C and 184B if oil elevations C and E are both outof service; secondly, through the line defined by switches 188B, 188Dand 184B if elevation C is in service but neither mills 42B or 42E areavailable for service and oil elevation E is out of service; thirdly,through the line defined by switches 188B, 188D and 188F if either orboth oil elevations C and E are in service but none of the mills 42B,42D nor 42F are available for service; and fourthly, through the linedefined by switches 184C, 188D and 188F if oil elevation E is in servicebut mills 42D and 42F are not available for service and oil elevation Cis not in service. This sub-circuit, 176, also contains parallellyconnected switches 186K and 188H that connect with mill operator relayK. Thus relay 180K will receive the energized pulse by one of the fourroutes described above if, in addition, its associated mill 42K isavailable for service but mill 42H is not.

Mill Starr Control Circuit FIGURE 8 is a schematic representation of aMill Start Control Circuit as employed in the present invention. Thecircuit shown typifies the control arrangement provided for placing oneof the pulverizing mills 42 in operation. In the described embodiment ofthe invention ve such circuits are employed but, in order to avoidduplication only one is described here. The -Mill Start Control Circuitcomprises a plurality of parallelly connected sub-circuits 190 through.202, each of which controls various aspects of the start-up program ofthe associated mill 42. Sub-circuit 190 contains parallelly connectedswitches operated by the feedback signals from t'he several componentsassociated with sensing apparatus of each mill. The sensing means areadapted to register each of the several mill permissives that must besatised prior to the mill being permitted to be placed in sevice. Forthe sake of brevity only ve such switches are shown in sub-circuit 190,these Ibeing switch 204 that Ireceives a feedback signal from the coldair gate'76 indicating that it is open; switch 206 that receives afeedback signal from the mill discharge valve 72 indicating that it isopen; switches 208 and 210 that indicate that the feeder inlet andoutlet gate valves 60 and 62, respectively, are open; and switch 282which is actuated by relay 280 to indicate that the mill is not lockedout. With the exception of switch 282 these feedback signals can beconveniently obtained from limit switches on the respective valves thatare closed when the valve is in its open position. In actual practice,several other similarly connected switches indicating other permissiveconditions are included in the sub-circuit Iand must be closed beforelthe mill can be considered as being ready for service. Such permissiveconditions include: the mill temperature is normal; adequate lubricatingoil and cooling water are available; seal air Iand tramp iron valves areopen; etc. When all of the permissive conditions are satisfied thecircuit is completed through sub-circuit 190 to Mill Ready Relay 212,thereby effecting actuation of the relay to close switch 214 insub-circuit 192. Actuation of Mill Ready Relay 212 indicates that allpermissives required for safe operation of the associated mill 42 aresatisfied. If any one of the conditions is not satistied, theappropriate s-witch will remain open thus prevention relay 212 frombeing actuated.

Sub-circuit 192 contains Mill Available Relay 216 connected in serieswith switches 214 and 218. Switch 214, as mentioned above, is associatedwith the Mill Ready Relay 212 and is closed upon energization of thatrelay. Switch 218 is a normally closed switch that is associated withrelay 272 (FIGURE 10) in sub-circuit 202, to be opened when theassociated mill is placed in service. Thus, completion of sub-circuit192 will energize relay 216 when the permissive conditions of theassociated mill are all satisfied and provided that the mill is notalready in service. As shown in FIGURE 11, the Mill Available Relay 216operates several other switches which 'have been referred tohereinabove. These switches include switch 126 in the Pulse InitiationCircuit of FIGURE 5, switches 160 and 162 in the Oil Elevation SelectionCircuit and switches 186 `and 188 in the Mill Selection Circuit.

Sub-circuit 194 contains the motor drive of the mill operator timer 220connected in series with switches 222, 224 and 226. Switch 222 is anormally open switch `operated by the associated Mill Available Relay216, switch 224 is a normally open switch operated by relay 132 (FIGURE9) in the associated Burner Counting Circuit which is closed when thereis suicient ignition energy available to ignite the coal burners 34, andswitch l l 226 is a normally open switch operated by the associated MillOperator Relay 180 of the Mill Selection Circuit. Completion ofsub-circuit 194 will effect re-set and start of the timer 220 which isset to have a timing duration of at least 12() seconds. During thisperiod each of the various steps attendant to mill start-up are etectedin response to the sequenced actuation of each of the timer contacts228, 239, 232 and 234 which may be operated by timer cams or the like.Thus, closure of timer contact 228 in sub-circuit 196 will energizeparallelly connected solenoids 244er, 244]), 244e and 244d to open thecoal burner inlet gate valves 46 that control admission of coal to theburners 34 in the associated coal Eburner elevation. Sub-circuit 198contains relay 257 connected in series with timer contacts I230` andswitches 248, 250 and 252. Timer contact 230 is set to closeapproximately l seconds after the closure of contact 228 in sub-circuit196. Switches 248 are normally open limit switches that are closed wheneach of the associated gate valves 46 is opened. Switches 250 and 252are associated with the Mill Ready Relay 212 and Burner Counting CircuitRelay 232, respectively. The presence of these two switches insub-circuit 198 ensures an immediate cessation of the mill start-upprocedure upon the occurrence of any conditions that would remove theassociated mill from its ready status as indicated by a de-actuation ofrelay 212 or upon the loss of ignition energy as indicated bydeactuation of relay 132. Completion of sub-circuit 198 electsenergization of relay 246 to simultaneously actuate the mill motor 254and hot air gate solenoid 256 by the closure of switches 258 and 260,respectively. Energization of relay 246 also effects closure of switch262 in subcircuit 208 which arms the Feeder Motor 264. The Feeder Motor264 will be started upon actuation of relay 262 upon the expiration ofapproximately l seconds after the mill motor 245 is energized when timercontact 240 is closed, completing sub-circuit 200. Again, actuation ofFeeder Motor 264 is contingent upon the Mill Ready Relay 212 and burnercounting circuit relay 132, both remaining energized to close switches268 and 270. Subcircuit `202 contains relay 272, indicated as theMill-in- Service Relay, which is armed -by the actuation lof the relay266 and energized by closure of timer contact 234 which occursapproximately 60 seconds after the closure of timer contact 232.Energization of relay 272 opens the normally closed switch 218 insub-circuit 192, thereby de-energizing the Mill Available Relay 216 t0open switches 162, 188 and 217 and close switches 126, 160` and 186.

Energization of the Mill-in-Service Relay 272 also opens contacts 276 insub-circuit 203. Sub-circuit 203 contains relay 280 which is seriallyconnected with switch 276 and timer contact 278. The relay 280` isindicated as the Mill Lockout Relay and is adapted to actuate switch 282in sub-circuit 190 to the open position whenever the Milln-Service Relay272 fails to be energized. Timer contact 278 is set to closeapproximately ve seconds after the closure of contact 234. Thus, if themill startup procedure fails to be completed for any reason, the relay272 will not be energized but instead relay 280 will be energized toopen switch 282 in sub-circuit` 190 and thereby de-energize Mill ReadyRelay 212 and `thence Mill Available Relay 216.

Control System Operation The operation of the control system as appliedto the herein described vapor generator fuel burner system will now bedescribed. For the purpose of description, it will be assumed first thatvapor generator start-up is initiated from a cold condition and that allof the pulverizing mills 42 are in operational condition and thereforeavailable for service. The vapor generator, being placed in service froma cold condition, must first undergo warm-up, or a gradual applicationof heat, in order that the various pressure parts of the unit are notsubjected to undue thermal Cil stresses. Warm-up is accomplished bysupplying water to the tubes 12 and fuel oil to one of the oil burnerelevations C, E or J. Heat is gradually increased within the furnace 22by increasing the flow of oil through the regulator valve in the mainoil line 50. As warm-up temperature requirements increase, additionalelevations of oil burners are placed in service by means of anindependent sub-loop that does not form part of this invention.

When the warm-up phase has been completed the power plant is thencapable of being placed on line in the power system. This isaccomplished when the output voltage of the electric generator 16 isplaced in phase with that of the power system. Upon this occurrence thepower plant is considered to be operating under normal conditions and itis at this point that the Fire Control 186 of the present inventionbecomes operative to control the placement of the several coal burnerelevations B, D, F, H and K in service.

Referring now to the various circuits that comprise the Fire Control 106under the conditions specified, namely that all of the oil elevations C,E and J are in operation and none of the pulverizing mills 42 have asyet been placed in service but are capable of being placed in service,the status of the electrical switches in the various portions of thecontrol circuit will be as follows. The actuation switch 110 in thePulse Actuation Circuit will be in the on position and the Fire Control106 thereby operative. In the Mill Start Sub-Loop (FIGURE 8) associatedwith each mill 42 all of the switches in the subcircuit 19t) will beclosed and the Mill Ready Relay 212 energized since all of thepermissives for safe mill operation are satisfied. Also, since theassociated mill 42 is not in service, the Mill-in-Service Relay 272 isde'energized and its associated switch 218 in sub-circuit 192 thereforeclosed. Moreover, with the respective Mill-in-Service Relays 272de-energized, switches 118B through K in line 112 of the PulseInitiation Circuit will be closed and switches 124B through K in line114 of that circuit will be open. With the Mill Ready Relay 212energized and the Milln-Service Relay 272 de-energized, switches 214 and218 in sub-circuit 192 of the Mill Start Sub-Loop will be closed and thecircuit complete to the Mill Available Relay 216 to close switch 217 insub-circuit 194. In addition, energization of the respective MillAvailable Relay 216 effects closure of switches 126B through K in thePulse Initiation Circuit, closure of switches B through K and opening ofswitches 162B through K in the Oil Elevation Circuit (FIGURE 6) andclosure of switches 186B through K and opening of switches 188B throughK in the Mill Selection Circuit (FIGURE 7). Since all of the oilelevations C, E and J are in operation, the burner counting circuitrelays 132 are de-energized and thus switches 128C, 128E and 128] in thePulse Initiation Circuit are all closed; switches 156C, 156B and 156]are closed and switches 158C, 158E and 158] are open in the OilElevation Selection Circuit (FIGURE 6); and switches 182C, 182B and 182]are closed and switches 184C, 184B and 184] open in the Mill SelectionCircuit (FIGURE 7).

Referring again to the Pulse Initiation Circuit (FIG- URE 5), when theoutput valve of the electric generator 16 is brought in phase with thatof the power system, switch 116 in line 112 is closed. If, at thispoint, load demand on the unit is suiciently low and capable of beingcarried by the operation of the oil burners 36 in oil elevations C, Eand J, the load will be so carried under the control of the CombustionControl 20 and the Fire Control 106 will remain ineiective. As the -loaddemand increases, however, the oil ow through line 50 will be increasedby operation of the oil ow regulator 90 under the control of theCombustion Control 20 until such time as the heating value of the oilbeing passed to the burners corresponds to that of the sum of theheatingJ values of the coal to be supplied by one pulverizing mill 47operating at minimum output plus that of its supporting oil whereuponswitch 120 operated by ow sensor 92 will close and a circuit will beestablished through line 112 to the operating motor of the pulse timer108. Upon energization, the pulse timer 108 is immediately re-set to itsstart position followed by commencement of its timing functioncomprising the intermittent closure of switch 136 for two secondsduration every 60 seconds, thereby effecting the pulsed closure ofswitches 140 and 142 in the Oil Elevation Selection Circuit and the MillSelection Circuit. The operation of the pulse timer 108 is such that itwill continue to emit periodic pulses until such time as the conditionthat effected energization of the timer has been removed. That is,barring loss of availability of all of the pulverizing mills 42 or ofthe oil burner elevations, the timer 108 will continue to pulse theswitches 140 and 142 until, with no mill already in service, a mill isplaced in service whereupon the circuit through line 112 in the PulseInitiation Circuit would be open, or, with at least one mill already inservice, the average mill loading of all of the mills in service fallsbelow 80% of their rate of capacity as determined by the CombustionControl 20, whereupon the circuit through line 114 will be opened.

With reference to FIGURE 6, the pulsed closure of switch 140 by thepulse timer 108 is transmitted to oil elevation operator relay 154Cthrough sub-circuit 164 since, under the conditions specified above,this is the only circuit that will be completed by the closure ofswitches 156 and 160 and the opening of switches 158 and 162. Actuationof relay 154C would normal-ly be effective to initiate operation of oilelevation C but, in view of the fact that the oil elevation is alreadyoperating, as a result of having remained in operation after the warm-upphase of unit operation was completed, pulsation of relay 154C will haveno effect. Instead, the pulsed closure of switch 142, which occurssimultaneously with switch 140, will be effective to transmit the pulsethrough sub-circuit 170 to mill operator relay 180D. Since all switches182 and 186 in the Mill Selection Circuit are closed at this time andswitches 184 and 188 are open, sub-circuit 170 is the only sub-circuiteffective to pass current and therefore relay 180D is the only milloperator relay that can be energized. Actuation of mill operator relay180D pulses the Mill Start Pulse Switch 226 in sub-circuit 194 of theMill Start Control (FIGURE 8) associated with mill 42D which suppliescoal to the coal burners 34 in elevation D. Closure of switch 226completes the circuit through subcircuit 194, switches 217 and 224having been closed beforehand by the energization of Mill AvailableRelay 216 and de-energization of oil burner counting circuit relay 132thereby actuating mill operator timer 220 which remains energized afterits actuating pulse terminates to effect the sequence closure of itsassociated contacts 228 through 234.

The operation of the mill operator timer 220 proceeds with rst, theclosure of contact 228 in sub-circuit 196 ten seconds after the timer isinitially energized, thereby actuating solenoids 244 to open each of theinlet gate valves 46 associated with the burners 34 in elevation D. Whenvalves 46 reach their open position, limit switches 248 associated witheach of the respective burners in subcircuit 198 are closed. Switches250` and 252 in sub-circuit 198 will be closed as long as the Mill ReadyRelay 212 associated with mill 42D remains energized and the burnercounting circuit relays 132 associated with oil burner elevations C or Eremain de-energized. The presence of these switches in sub-circuit 198and comparable switches 268 and 270 in sub-circuit 200 serve toterminate the mill start-up procedure in fthe event of the loss of oneor more of the permissive conditions for safe mill operation after themill operator timer 220 has been energized. Timer contact l230 closesten seconds after the closure of contact 228 and, if all of the burnerinlet gates have opened, the circuit is complete to the Mill MotorActuator Relay 257, the energization of which simultaneously actuatesMill Motor Start Switch 258 and the Hot Air Gate Solenoid Switch 260 t-ostart the motor 56 and energize Hot Air Gate Solenoid 256 to open theHot Air Gate Valve 68 associated with mill 42D. Energization of relay257 also closes the Feeder Motor Arm Switch 262, in subcircuit 200. Thissub-circuit is completed 30 seconds after the actuation of re-lay 257 bythe closure of Timer Contact 232, it having been determined that 30seconds is sufficient time within which to pass an adequate supply ofair to the mill for etlicient operation thereof. Completion ofsub-circuit 200 effects energization of the Feeder Motor Start Relay 266which closes Motor Start Switch 267, thereby actuating the Feeder Motor54 to supply raw coal to the pulverizing mill 42D. Relay 266 also servesto actuate switch 274 in sub-circuit 202 to the closed position to armthe Mill-in-Service Relay 272 which is energized 60 seconds after theactuation of the Feeder Motor 54 upon closure of Timer Contact 234.Energization of relay 272 actuate-s switch 218 in sub-circuit 192. ofthe Mill Start Control Circuit to the open position, therebyde-energizing the Mill Available Relay 216 to open switch 217 insub-circuit 194, switch 126D in the Pulse Initiation Circuit (FIGURE 5),switches 160D in the Oil Elevation Selection Circuit (FIGURE 6) andswitch 186D in the Mill Selection Circuit (FIGURE 7) while closingswitch 162D in the Oil Elevation Selection Circuit and switch .188D inthe Mill Selection Circuit. Ene-rgization of relay 272 also serves toopen switch 118D in line 112 of the Pulse Initiation Circuit and toclose switch 124D in line 114, thereby de-energizing the pulse timer 108and transferring all subsequent control of the mills from line 112 ofthat circuit to line 114.

If, for any of a number of reasons, mill 42D is unable to be placed inservice, the Mill-in-Service- Relay 272 would remain de-energized andiive seconds later upon closure of Timer Contact 27'8, Mill LockoutRelay 280 would be energized to open switch 282, thereby de-energizingMill Ready Relay 212 and Mill Available Relay 2.16. De# energization ofthe Mill Available Relay 216 would effect -opening of switches 126D inthe Pulse Initiation Circuit, D in the Oil Elevation Selection Circuitand 186D in the Mill Selection Circuit and closure of switches 162D inthe Oil Elevation Selection Circuit and 188D in the Mill SelectionCircuit. Failure of the Mill-in-Service Relay 272 associated with mill42D to energize would maintain the pu'lse time-r 108 in an energizedcondition since the switches in line 112 of :the Pulse InitiationCircuit would remain closed. Therefo-re, the Pulse Selection Circuitwould be pulsed again by another closure of switch 142.. Since switch186D in the Mill Selection Circuit is now opened and switches 188Dclosed the pulse would be transmitted to mill selection re-lay B whichwould initiate start-up of mill 42B that supplies pulverized coal to theburners of coal elevation B by means of the Mill Start-up ControlCircuit (FIGURE 8) associated with mill 42B in the same manner aspreviously described for start-up of mill 42D.

Similarly, if mill 42B failed to 'be placed in service', its MillLockout Relay 280 would be energized 115 seconds after the initiation ofthe second pulse :t-o effect opening of switches 126B in the PulseInitiation Circuit, 186B in the `Oil Elevation Selection Circuit and186D in the Mill Selection Circuit while closing switches 162B in theOil Elevation Selection Circuit and 188B in the Mill Selection Circuit.Since no mill has yet been placed in service, the pulse timer 108 wouldremain energized and still another pulse would be generated to closeswitch 142. Closure of switch 142 would now generate a pulse that wouldbe transmitted to the mill selection relay 180F and thereafter to millselection relays 180H and 180K in seque-nce in the event the previousmill in the sequence failed to be placed in service.

Assuming mill 42D was successfully placed in operation, pulverized coalis supplied to the burners 34 in coal elevation D :through theassociated coal supply line 44. In the furnace the coal is ignited bymeans of the ignition energy provided by the lburners 36 in oilelevations C and E thus placing the first coal elevation in service. Itshould be noted that ignition of the coal issuing from an elevation ofcoal burners 34 can be accomplished from the combustion energy providedby a single elevation of oil burners. Due to the physical arrangement ofthe burner assembly 32, coal elevation D is located intermediate oilelevations C and E and there-fore can obtain ignition energy from one orboth groups of oil burners.

When mill 42D is placed in service, switch 118D in line 112 of the PulseInitiation Circuit is actuated .to the open position lby Mill-in-ServiceRelay 272, thereby breaking the circuit and de-energizing the pulsetimer 108. At the same time switch 124D in line 114 is closed totransfer operati-on of the pulse timer 108 from line 112 to thecircuitry of line 114. After the mill and its associated elevation ofcoal burners has once been placed in service operation proceeds undercontrol of the Combustion Control which regulates the supply of coal tothe mill .and thence to :the burners in response to load de-mand on theunit. The Combustion Control 20 is also effective at this point tofirst, actuate the main oil supply valves 96 in the three oil burnerelevations to the closed position, thereby lterminating the ow of oilthrough these valves. Oil continues to fiow, however, through each ofthe bypass fiow regulations 94 such that oil, at minimum pressure,continues to fiow to the oil burners 36. This oil flow is sufiicient tomaintain 4a arne at the burners and to provide sufficient ignitionenergy to an adjacent group of coal burners to sustain their ignition.Following this, the Combustion Control 20 operates to close the lbypassvalve 94 associated with all but the oil burner elevation associatedwith the burners 34 of oil elevation D, namely oil elevation C. Thetermination of oil fiow tothe 'burners 36 in this man- .ner isaccomplished by means of a control sub-loop of Combustion Control 20which is not considered germane to the present invention and thereforeis not described herein.

At this point, the regulation of the operation of the mill 42D is underthe control of Combustion Control 20. As load demand on the unit rises,the speed of motor 54 driving the feeder 52 associated with mill 42D isincreased to deliver coal at an increased rate to the mill. When theload on the mill reaches 80% of its rated capacity as measured by thetachometer 64, switch 122 in line 114 of the Pulse Initiation Circuit isclosed to energize the pulse timer relay 108, thereby re-setting it andthereafter initiating its timer operation to energize relay 138 andsimultaneously pulse switchesr 140 and 142 that operate the OilElevation Selection Circuit and Mill Selection Circuit, respectively, atthe rate of one pulse every 6() seconds.

In the Oil 4Elevation Selection Circuit (FIGURE 6) closure of switch 140will transmit current to relay 154C since switches 160B and 156C areclosed, mill 42 bein-g available for service and Oil Elevation Circuitnot being locked out of service. But, since oil elevation C is alreadyin operation energization of relay 154C will have no effect. In the MillSelection Circuit (FIGURE 7), however, closure of switch 142 willcomplete sub-circuit 172 to energize relay 180B since switch 132C isclosed because the Oil Elevation Circuit is delivering sufiicientignition energy with which to ignite its associated coal burners, andswitch 188D is closed because mill 42D is now in service and thereforeno longer available to be placed in service. Switch 188D was closed whenrelay 217 associated with mill 42D was de-energized and switch 186B isclosed because relay 217 associated with mill 42B is energized due tothe fact that its mill operator relay 180B is energized and switch 218,indicating the mill is not in service, is closed. Energization of millstart relay 180B pulses switch 226 in sub-circuit 194 of the MillSelection Circuit (FIGURE 8) associated with mill 42B to energize timer220 and thereby initiate the start-up sequence for mill 42B. Thestart-up sequence of this mill thereafter proceeds in the same manner asearlier described with regard to the start-up of mill 42D. Uponcompletion of the start-up sequence, Mill-in-Service Relay 172 isenergized opening switch 218 in sub-circuit 192 to de-energize MillAvailable lRelay 216, as well as opening switch 118B in line 112 of thePulse Initiation Circuit and closing switch 124B in line 114. When theMill Available Relay 216 is de-energized, switch 126B in the PulseInitiation Circuit, switch 160B in the Oil Elevation Selection Circuitand switch 186B in the Mill Selection Circuit are closed and switches162B in the Oil Elevation Selection Circuit and 188B in the MillSelection Circuit opened, thereby arming the selection circuits for thenext pulse generated by the pulse timer 10S.

When the burners 34 of coal elevation B are placed in service, switch122 in line 112 of the Pulse Initiation Circuit is opened since thereare now two mills in service and their average load will be less thanthe required to close the switch. The opening of switch 122 opens thecircuit through line 114, thereby de-energizing the pulse timer 108.

In the event that mill 42B is unable to be placed in service, eitherbecause its permissive conditions are not satisfied or because componentmalfunction occurred after the sub-circuit sequence was initiated, theMill Available Relay 216 `will be de-energized to close switches 160Band 186B and also switches 162B and 188B in the respective selectioncircuits. if the former occurs the failure of one or more of theswitches 204 through 21) in sub-circuit 190 to close would prevent theMill Ready Relay 212 from being energized. If the latter occurs MillLockout Relay 280 will be energized to open switch 282 in sub-circuit190 and de-energize the Mill Ready Relay 212. Such occurrence wouldnecessitate placing Ianother elevation of oil burners 36 in servicebefore another elevation of coal burners 34 could be placed in operationdue to the fact that oil elevation C is capable of providing ignitionenergy only for the burners 34 of coal elevations B and D. Therefore,before coal elevation F can become operational the burners 36 in oilelevation E must be placed in service in order to provide ignitionenergy for the elevation F coal burners.

Placing oil elevation E in service is accomplished by the pulse closureof switch 140, which pulse is transmited to oil elevation start relay154B to effect start-up of the pilot torches 40 associated with thatelevation and admit lfuel to the oil burners thereof. This isaccomplished by the fact that with oil elevation C operati-ng. mill 42Din service and mill v42B not capable of being placed in service,sub-circuit 166 in the Oil Elevation Selection Circuit is now renderedeffective to transmit the pulse from switch to the relay 154E throughswitches 162B, 162D, 160]? and 156B all of which are now closed.Switches 162B and 162D lare closed because their associated MillAvailable Relays 216 are de-energized. Switch F is closed because itsassociated rel-ay 21-6 is energized and switch 156B` is closed becauseits associated burner counting circuit relay 132 is de-energizedindicating that oil elevation F is not locked out of service. Thus,energization of Pulse Timer Relay 138 by the timer 108 will pulse switch140 to the closed position, which pulse will then be transmitted torelay 154B to initiate start-up of the burners 36 of oil elevation E.Start-up of the oil elevation is effected by first 'actuating theElevation Inlet Gate Valve 98 and the pilot torch fuel valves 102 totheir open positions and thereafter ener- -gize the spark ignitors 104to ignite the torches which, in turn, ignite the oil issuing from theburners 36. When the oil elevation is placed in service switches 182Bare then closed and s-witches 184B are opened in the Mill SelectionCircuit. The length of time required to place an oil elevation inservice is approximately 50 seconds. Therefore, when the next pulse isgenerated by the pulse timer 108, 60 seconds after the previous pulse,sub-circuit 174 will then be effective to transmit the pulse from 17 theswitch 142 through switches 188B, 188D, 182B and 186F to mill startrelay 180B. When relay 180F is energized to actuate the Mill StartControl associated with mill 42F start-up of the mill will thereafterproceed in the same manner as previously described with regard to thestart-up of mill 42D.

When the mills 42B and 42D and the coal burners 34 supplied by them inelevations B and D are in operation and a further increase in loaddemand requires that another elevation of coal burners 34 be placed inservice, mill 42F will be placed in service in the same manner asdescribed above with the first pulse generated by the pulse timer 1118being transmitted to the oil elevation start relay 154B and the nextpulse then transmitted to the mill start relay 1801:. Sub-circuit 164can no longer transmit the pulse since mills 42B and 42D are inoperation and switches 160B and 160D are therefore open. Similarly,sub-circuit 168 cannot transmit the pulse since oil elevation E is notlocked out of service and mill 42F is available for service and switches158B and 162F are therefore open. Thus, upon the pulsed closure ofswitch 140, current can only pass through switches 162B, 162D, 160F and15615 to relay 154E thus initiating the start-up of the burners 36 ofoil elevation E. When the pulse timer 108 generates the next pulse it istransmitted from switch 142 in the Mill Selection Circuit throughsub-circuit 174 c011- taining switches 188B, 188D, 182B and 186F whichare all closed to energize the relay 180F in the same manner as wasdescribed above and start-up of mill 42F will then proceed accordingly.

With coal elevations B, D and F in operation the need for an additionalelevation of coal burners to be placed in service due to a furtherincrease in load demand will be satised by start-up of the burners 36 ofoil elevation J followed by the placement of mills 42H and 42K inservice. According to the desired sequence mill 42H will be placed inservice rst but if, however, that mill is unable to be placed inservice, mill 42K will then be rendered effective to be placed inoperation. This occurs as follows. The pulse generated by the pulsetimer 108 upon closure of switch 122 in the Pulse Initiation Circuitwill be transmitted upon closure of switch 140 through subcircuit 168 tooil elevation start relay 154]. The pulse will be passed throughswitches 162B, 162F, 162D, 160H, 160K and 156] all of which are closeddue to the fact that mills 42B, 42D and 42F are now in service andtherefore are not available to handle the additional load s that theirrespective relays 216 are de-energized and the switches 162 associatedwith these relays are therefore closed. Since mills 42H and `42K areeach available for service their associated relays 216 will be energizedso that switches 16() associated with these relays are closed. Since oilelevation J has not been locked out of service, its associated burnercounting circuit relay 132 will be de-energized such that switch 156]will be closed. After the burners 36 of oil elevation J are placed inservice, the next pulse generated by the pulse timer 8 will betransmitted through switches 188B, 188D, 188F, 182] and 186H ofsub-circuit 17 6 and the Mill Selection Circuit to the mill start relay180H which is effective to initiate start-up of mill 42H.

Current will not pass to relay 130K if mill 42H is available for servicesince switch 188H would then be open. lf, however, mill 42H were notavailable for service, switch 186H would be open, thereby preventingenergization of relay ISDH and switch 188H, being operated by the samerelay but having the opposite sense of switch 186H would be closedthereby effecting energization of relay 189K to initiate start-up ofmill 42K.

After mill 42H has been placed in service switch 186H is caused to beopened by the actuation of relay 272 in sub-circuit 202 which, in turn,opens switch 218 in subcircuit 192 to de-energize the relay 216. Theopening of switch 186H effects closure of switch 188H thereby armingrelay 180K to enable it to receive the next pulse generated by the pulsetimer 108. Thus, upon a further increase in load demand requiring theplacement of yet another elevation of coal burners in service,energization of the pulse timer 108 will effect the generation of apulse that will be received by relay K to initiate start-up of mill 42Kand the placement of coal burners 34 of elevation K in service.

There has thus been described an electro-mechanical control system forautomatically controlling the start-up of burners of a coal-tired,multi-burner vapor generator that is characterized by simplicity ofdesign and efficiency and flexibility of operation. By means of thepresent invention the plurality of coal pulverizing mills that governthe operation of the coal burners in the fuel burning system of a largecapacity vapor generator can be manipulated to place only that elevationof coal burners in service that is capable of being operated safely. Thesystem also provides means for ensuring that the increase in load demandis satisfied in the event that the selected burner elevation cannot beplaced in service by automatically selecting another elevation andplacing it in service. The invention, when employed in conjunction withanalog controls for regulating the performance of the burners after theyare once placed in operation, is operable to achieve total automation ofthe burner systems of large capacity vapor generators.

It will be understood that various changes in the details, materials,and arrangements of parts which have been herein described andillustrated in order to explain the nature of the invention, may be madeby those skilled in the art within the principle and scope of theinvention as expressed in the appended claims.

What is claimed is:

1. A fuel burning system having primary burner means, secondary burnermeans adapted to provide ignition energy for said primary burner means,coal pulverizing mill means connected with said primary burner means forsupplying fuel thereto, signal responsive actuator means operativelyassociated with said mill means and said secondary burner meansrespectively for placing each in operation, and control means operatingsaid actuator means for automatically placing said primary burner meansin service in response to the need for operation thereof, said controlmeans comprising:

(a) first circuit means operatively connected to said secondary burneractuator means and adapted to energize said actuator means upon receiptof -a pulsed signal;

(b) second circuit means operatively connected to mill actuator meansand adapted to energize said actuator means upon receipt of a pulsedsignal;

(c) said second circuit means including means preventing theenergization of said mill actuator means until after said secondaryburner means are established in operation;

(d) means responsive to the need for operation of said primary burnermeans and adapted to emit a signal in response thereto;

(e) means operated by said need responsive signal for generating aperiodically pulsed signal;

(f) and 'means for simultaneously transmitting said pulsed signal tosaid rst and second circuit means for actuating said secondary lburnermeans and thereafter, said mill means.

2. Apparatus as recited in claim 1 including:

(a) load demand indicator means adapted to emit a a signal at apredetermined value of load demand;

(b) means for transmitting said load demand signal to said pulsed signalgenerating means for operating the same.

3. Apparatus as recited in claim 1 including:

(a) a plurality of primary burners arranged in groups;

(b) a coal pulverizing mill operatively associated with each group ofprimary burners;

(c) means responsive to the need for operation of said lprimary burnerscomprising circuit means for operating said pulsed signal generatingmeans including:

(i) tirst and second lines each responsive to different need conditionsof said system and each being adapted to transmit :a signal to energizesaid pulsed signal generator upon the occurrence of the respective needconditions;

(ii) and means for rendering said first line operative when none of saidprimary burner groups are in operation and for rendering said secondline operative when at least one of said primary burner groups Iare inoperation.

4. Apparatus as recited in claim 3 including:

(a) load demand indicator means adapted to emit a signal at apredetermined value of load demand; (b) means for transmitting said loaddemand signal `to said pulsed signal generating means through saidsecond line.

5. Apparatus as recited in claim 1 including:

(a) a plurality of primary burners arranged in groups;

(b) a plurality of secondary burners arranged in groups and each adaptedto provide ignition energy for an associated group of primary burners;

(c) a coal pulverizing mill associated with each primary burner groupfor supplying 4fuel thereto; (d) independently operated actuator meansassociated with each of said pulverizing mills and secondary burnergroups;

(e) said first and second circuit vmeans comprising:

(i) means operative to transmit said pulsed signal to the actuator of asingle secondary burner group according to a preselected sequence;

(ii) and means for transmitting .a subsequent pulsed signal to theactuator of a pulverizing mill operating a group of primary burnersassociated with said single secondary burner group.

6. Apparatus as recited in claim 5 including:

(a) means preventing the energization of each of said -actuators of saidpulverizing mill and said secondary burner groups upon failure of thesame to satisfy predetermined permissive conditions;

(b) means for transmitting a pulsed signal to the actuator of anothersecondary burner group upon failure of the selected actuator to beenergized;

(c) and means for transmitting a subsequent pulsed signal to theactuator of a pulverizing mill operating a group of primary burnersassociated with said other secondary burner group.

7. Apparatus as recited in claim 6 including:

(a) means for transmitting a pulsed signal to the lactuators of all ofsaid secondary burner groups in sequence;

(b) means for terminating the transmission of -a pulsed signal to saidsecondary burner group actuators upon the energization of one of saidactuators;

(c) and means for transmitting a subsequent pulsed signal to theactuator of a pulverizing mill operating a group of primary burnersassociated with said actuated secondary burner group.

8. Apparatus as recited in claim 5 wherein said first circuit meanscomprises:

(a) a plurality of subcircuts, each adapted to energize an actuatorassociated with one of said secondary burner groups;

(b) each of said subcircuts including:

(i) means responsive to the operability of the associated secondaryburner group for transmitting said pulsed signal to said yactuator onlywhen said associated secondary burner group is operable;

(ii) and means responsive to the availability of the pulverizing millsoperating the primary burner associated with said secondary burner groupfor transmitting said pulsed signal to said actuator only when saidassociated pulverizing mill is available for service.

9. Apparatus as recited in claim 8 wherein each of said subcircutsincludes means for transmitting said pulsed signal to the actuator ofthe associated secondary burner group only when the actuator for openingthe previous secondary burner group in said sequence fails to receivesaid pulsed signal.

10. Apparatus as recited in claim 8 wherein said second circuit meanscomprises.

(a) a plurality of subcircuts each adapted to engage an actuatorassociated with one of said pulverizing mills;

(b) each of said subcircuts including:

(i) means responsive to the operation of a secondary burner groupassociated with the primary burner group operated by said pulverizingmill for transmitting the pulsed signal to the mill actuator only whensaid associated secondary burner group is in operation;

(ii) and means responsive to the availability of the associatedpulverizing mill for transmitting said pulsed signal to the actuator ofsaid associated mill only when said mill is available for service.

11. Apparatus as recited in claim 10 including:

(a) a pair of primary burner groups capable of being ignited by each ofsaid secondary burner groups;

(b) means for transmitting said pulsed signal to the actuator of thepulverizing mills operating one of said primary burner groups when theassociated secondary burner group is operating;

`(c) and means for transmitting said pulsed signal to the actuator ofthe pulverizing mill operating the other of said primary burner groupswhen said one actuator fails to be energized.

12. Apparatus as recited in claim 5 including:

(a) electrically operated actuators;

(b) first sensing means for sensing the operability of each of saidsecondary burner groups;

(c) second sensing means for sensing the avaliability for service ofeach of said pulverizing mills;

(d) third sensing means for sensing the state of operation of saidsecondary burner groups;

(e) first circuit means including a plurality of parallelly-connectedsubcircuts each operating one of said secondary burner group actuatorsand each containing means to pass an electric current to said actuatorwhen said tirst sensing means indicates the associated secondary burnergroup is operable and said second sensing means indicates the associatedpulverizing mill is available for service;

(f) second circuit means including a plurality of parallelly-connectedsubcircuts each operating one of said pulverizing mill actuators andeach containing means to pass an electric current to said actuator whensaid second sensing means indicates the associated pulverizing mill isavailable for service and said third sensing means indicates theassociated secondary burner group is operating;

(g) pulse generating means for simultaneously transmitting a periodicelectric pulse to said rst and second circuit means;

(h) and means responsive to the needs for operation of an additionalprimary burner group for energizing said pulse generating means.

13. Apparatus as recited in claim 12 including load demand sensing meansoperatively connected to said pulse generating means to energize thesame at a predetermined value of said load demand.

14. Apparatus as recited in claim 12 wherein the subcircuits comprisingsaid iirst circuit means each include,

in series:

(a) an electrically actuable relay for operating said secondary burnergroup actuator;

(b) first switch means responsive to said rst sensing means to be closedwhen the associated secondary burner group is operable;

(c) second switch means responsive to said second sensing means to beclosed when the associated pulverizing mill is available for service.

15. Apparatus as recited in claim 14 wherein means are provided foroperating said secondary burner group actuators according to apreselected sequence, said means comprising switch means having anopposite sense from said first and second switch means in the earliersubcircuits connected in successive subcircuits in series with the firstand second switch means in said successive subcircuits whereby anelectric current can pass through only one of said subcircuits at atime.

16. Apparatus as recited in claim 12 wherein the subcircuits comprisingsaid second circuit means each include, in series:

(a) an electrically actuable relay for operating said pulverizing millactuator;

burner group is established in operation.

References Cited UNITED STATES PATENTS 15 2,073,346 3/1937 Kuernpell10L-103X `CHARLES I. MYHRE Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION August 6, 1968Patent No. 3,395,657

Jack A. Schuss It is certified that error` appears in the aboveidentified patent and that said-Letters Patent are hereby corrected asshown below:

Column l, line 2l, "operation" should read operational Column 3, line24, "vales" should read valves line 70, after "oil" insert line Column9, line 47, after "182", cancel "L" and insert E -4 l Column l0, line38, "the" should read. this line 5l, "prevention" should Column l5, line26, "regulations" should read regulators Column 20, line 7, "opening"should read operating line ll, should read line l2, "engage" should readenergize Signed and sealed this 7th day of April 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

